Nuclear Counter Effect and Pion-Electron misidentification: Simulations and 1998 test beam results

The electron/charged pion discrimination within the ECAL is investigated using GEANT simulations and the 1998 test beam results. The Nuclear Counter Effect within the Avalanche Photo-Diodes enhances the probability of an electron misidentification. The test beam data show a Nuclear Counter Effect with a mean value of about 450 MeV for a Minimum Ionizing Particle crossing the APD, instead of the expected 200-250 MeV for a readout with a single APD. This value can be explained with the inefficient connection between crystals and APD`s in the PROTO 97 set-up. The pion beam data show a long tail in the E/p-ratio, which can be reproduced by GEANT simulations with Nuclear Counter Effect. GEANT simulations are then used for a study of the pion-electron confusion with the expected Nuclear Counter Effect and the foreseen set-up with two APD`s per crystal. These simulations show that the tail in the pion-energy deposition is still present. As a result one expects that about 0.1 % of the pions with 10 GeV < E < 100 GeV have E/p > 0.95 and are potential ``fake electrons'' candidates.